This invention relates to a cuff for blood pressure measuring devices, and more particularly to a cuff which is adapted to the detection of a pulse wave in a person's finger, rather than in an arm.
A cuff has been disclosed in the article "New oscillometric method for indirect measurement of systolic and mean arterial pressure in the human finger", Med. & Biol. Eng. & Comp., May 1982, pp. 314-318, which has disposed therein a light-emitting element and light-sensitive element opposing each other, in which the light emitted from the light-emitting element is received by the light-sensitive element after passing through the artery of a finger, thereby detecting a pulse wave. In this detector however, since the light must pass the distance corresponding to the width of the finger, it is difficult to achieve the sensitivity required for highly accurate measurement.
For this reason, the inventor of this application and their colleagues employed by their common assignee have devised an improved cuff, applications to which were filed on Apr. 11, 1986, assigned U.S. Ser. No. 850,819 and Nov. 24, 1986, assigned U.S. Ser. No. 933,892. In FIGS. 1(a) and 1(b) of prior application Ser. No. 850,819, a single light-emitting element 3 and a single light-sensitive element 4 are shown as mounted adjacent to each other on the inner surface of the cuff 2. The light emitted from the light emitting element 3 is reflected from the artery 6 of a finger 5 and received by the light-sensitive element 4. In this application the invention of prior application Ser. No. 850,819 is shown in FIG. 5, which is described further below.
In the cuff disclosed in Ser. No. 850,819, a light-path can be shortened because the light-emitting element and lightsensitive element are disposed close to the artery of the finger, so that the level of a pulse wave signal can be multiplied to improve the sensitivity. However, since the prior cuff has only a single pair of light-emitting and light-sensitive elements disposed close to each other, the detectable range of a pulse wave is limited as shown by the broken line in FIG. 5 of this application. Accordingly, a desired pulse wave as shown in FIG. 6 of this application cannot be detected unless the finger is inserted into a cylindrical space such that the artery 64 of the finger is covered by the limited detection range.
In addition, the location of the finger artery differs from person to person, which makes it difficult to guide the finger into an appropriate position for accurate measurement. Thus, as shown in FIG. 7 of this application, the finger is often inserted with its artery not covered by the detectable range. In this condition, the peak value of the detected pulse wave cannot be clearly identified as shown in FIG. 8 of this application, thus making it difficult to measure an accurate blood pressure.
Moreover, it is desirable to provide a means for triggering air into the cuff when desired. In order to avoid overpressurization of the cuff when not in use, a means is also provided for ensuring that air is exited from the cuff. Further, a means is provided for halting the pressurization of the cuff when desired.
It is, accordingly, an object of this invention to provide a cuff for blood pressure measuring apparatus which overcomes the above-mentioned disadvantages.
It is another object to provide a cuff for blood pressure measuring apparatus which is capable of detecting an appropriate pulse wave for accurate measurement.
It is still another object to provide a cuff for blood pressure measuring apparatus whose pulse wave detection range is expanded to cover finger arteries which are differently located from person to person.
According to one aspect of this invention, there is provided a cuff for a blood pressure measuring apparatus, which is made of flexible material, comprising an inner surface defining a cylindrical space for a finger to be inserted thereinto, an outer surface together with the inner surface defining a fluid chamber therebetween which applies pressure to the finger, a light-emitting element mounted on the inner surface for emitting light at the artery of the finger, a light-sensitive element mounted on the inner surface adjacent to the light-emitting element for receiving the reflected light from the artery, wherein a plurality of elements are provided at least either for the light-emitting element or for the light-sensitive element. That is, if one light-emitting element is employed, then at least two light-sensitive elements are used, and vice versa. The invention also incudes the use of two or more of each of the light-emitting and light-sensitive elements.
Further, the invention includes a microswitch operably connected to an air pump suitable for being triggered when air supply is required in the air chamber of the cuff. In order to trigger the microswitch, an actuator lever inside the cuff is provided for activating the microswitch when the finger is properly seated thereon. The actuator lever is provided in such a way that when the finger is not seated thereon, the actuator lever permits air to exit from the cuff to avoid undesired overpressurization of the cuff. The invention also includes a light emitting device (LED) and light receiving device (LRD) inside the cuff in order to control the air intake of the cuff when desired.
Other objects and numerous advantages of the cuff for blood pressure apparatus according to this invention will become apparent from the following description when considered in conjunction with the accompanying drawings.